Map-vs-native-cache.js

var Benchmark = require('benchmark');
var suite = new Benchmark.Suite;

var testArray = [];

for (var s = 0; s < 5000; s++) {
    testArray.push(Math.floor(Math.random() * 100));
}

console.log('Testing caching')
suite
    .add('Map', () => objectMap(testArray))
    .add('MapSingleAccess', () => objectMapSingleAccess(testArray))
    .add('Native', () => objectNative(testArray))
    .add('NativeSingleAccess', () => objectNativeSingleAccess(testArray))
    .on('cycle', event => console.log(String(event.target)))
    .on('complete', function() {console.log('Fastest is ' + this.filter('fastest').map('name'))})
    .run({ 'async': true });


function objectMap(arr) {
    var result = [];
    var cache = new Map();

    for(var i = 0; i < arr.length; i++) {
        var item = arr[i];

        if(cache.has(item)) {
            result.push(cache.get(item));
        } else {
            var a = Math.pow(item, 5) * 321312;
            cache.set(item, a);
            result.push(a);
        }
    }

    return result;
}

function objectMapSingleAccess(arr) {
    var result = [];
    var cache = new Map();

    for(var i = 0; i < arr.length; i++) {
        var item = arr[i];

        var cacheEntry = cache.get(item);
        if(typeof cacheEntry !== "undefined") {
            result.push(cacheEntry);
        } else {
            var a = Math.pow(item, 5) * 321312;
            cache.set(item, a);
            result.push(a);
        }
    }

    return result;
}

function objectNative(arr) {
    var result = [];
    var cache = Object.create(null);

    for(var i = 0; i < arr.length; i++) {
        var item = arr[i];

        if(item in cache) {
            result.push(cache[item]);
        } else {
            var a = Math.pow(item, 5) * 321312;
            cache[item] = a;
            result.push(a);
        }
    }

    return result;
}

function objectNativeSingleAccess(arr) {
    var result = [];
    var cache = Object.create(null);

    for(var i = 0; i < arr.length; i++) {
        var item = arr[i];

        var cacheEntry = cache[item];
        if(typeof cacheEntry !== "undefined") {
            result.push(cacheEntry);
        } else {
            var a = Math.pow(item, 5) * 321312;
            cache[item] = a;
            result.push(a);
        }
    }

    return result;
}

This benchmark does not show the whole story. Your key is just a number. Map is designed for strings keys.

Here is the better benchmark
https://jsbench.me/h1kje2tt1b